Primary aims of this continuing project include (1) ascertainment of the prenatal origins (antecedents) of typical and variable patterns of human postnatal dental development, and (2) the design of techniques which would correlate patterns of prenatal dental development, if possible, with neighboring dentofacial regions as well as with organs and body regions further removed from the dental region. Aim one has been implemented using "morphologic staging" and developing primary and secondary dentitions. Morphologic data on teeth were derived from serial histologic sections of over 685 human abortuses derive from documented pregnancies. Key time periods of dental development, ranging from tooth initiation to cusp calcification, were surveyed. Data were treated on an information background including sex, race, chromosome information (whenever possible), and pregnancy and family histories. This approach has demonstrated intra-individual and inter-individual (from same or differing families) comparisons as such considerations bear on specific tooth development dental assymetries, and sequence polymorphisms. The second aim correlates dentofacial development with development of key organs (e.g., heart, brain, thymus) and regions (e.g., hand-wrist) elsewhere in the abortus. This second aim allows a retrospective explanation (with supporting data) of why defects in the dentofacial area perhaps are often associated with specific defects elsewhere in the body. Moreover, background histories on family and chromosome for exmmple, allow explanation of defects as either isolated or familial events.